Usage of common household light bulbs (known in the industry as an “A-lamps”) and Compact Fluorescent Lamps (CFL) in table lamps and floor lamps accounts for a large portion of the energy consumed by such lamps. Table lamps and floor lamps are well established as domestic furnishings and thus likely to persist into the future notwithstanding introduction of new more efficient light source technology. Thus there is need to adapt new light source technology to these traditional portable fixtures types, and it would be more desirable to maximize efficiency and performance of new technology when used in these traditional portable fixtures.
Floor lamps and table lamps typically have a lamp shade that blocks a direct view of the light bulb, so as to prevent visual discomfort associated with glare. Typically, especially in the case of table lamps (though not universally), the lamp shade has a larger bottom aperture and smaller top aperture. Illumination passing through the bottom aperture provides task illumination that is useful for reading or performing other tasks when seated next to the lamp. Illumination passing through the top aperture is reflected off nearby walls and ceilings and provides indirect general illumination of the room. Lamp shades are generally not highly engineered optical control surfaces. Their main purpose is to prevent glare. A problem with lamp shades is that they create a light distribution which is very non-uniform and strongly peaked at the lamp itself and relatively weak 500 cm to 1 meter away where the light is likely to be most useful to a person seated in the vicinity of the lamp.
FIG. 1 is a schematic illustration of a typical table lamp 100 with a stem 102 extending upward from a lamp body 104 to an Edison socket 106 into which is screwed a light bulb 108. A harp 110 attached to the stem 102 connects to a frame 112 of a traditional lamp shade 114. The shade 114 includes a lower aperture 116 through which light passes to provide task illumination and an upper aperture 118. Dimensions are shown to give some context to the data shown in FIGS. 2-3. A radial axis, labeled R(cm) to denote measurement in units of centimeters, extends radially from the base of the lamp 100.
FIGS. 2 and 3 show illuminances (in units of lux) measured along the radial axis R(cm) with a light meter. The light meter sensor head was oriented facing straight up. FIG. 2 is for measurements with a lamp shade with highly reflective white liner and FIG. 3 is for measurements with a somewhat yellowed old lamp shade. In both FIGS. 2 and 3 the data represented by square symbol data points 202, 302 is for a traditional incandescent A-lamp and the data represented by the circle symbol data points 204, 304 is for a CFL. All four measurements showed a light distribution that was peaked at the lamp and undesirably dropped off to substantially lower levels at radial distances where the light would be useful to a person seated in the vicinity of the lamp.
Light Emitting Diode (LED) technology is a new technology for general illumination. However at present omnidirectional LED light bulbs intended to replace the common household light bulb are prohibitively expensive. Name brand LED A lamps presently sold in 2011 for between $40 to $50 each. One factor in the cost is that current designs use cast aluminum bodies. To make each lamp body, molten metal must be let into a mold, the mold allowed time to cool and the part extracted. Then each body must be individually handled in a machining operation to perform steps such as facing thermal mating surfaces and drilling and tapping holes used to secure Metal Core Printed Circuit Boards (MCPCBs) on which LEDs are mounted. It would be desirable to have designs for LED lamps that could be manufactured less expensively and therefore more suitable to mass production on a scale needed for consumer light bulbs. Another important factor in the high cost of LED based A-Lamps is the price of the packaged LED devices themselves. Power LEDs suitable for use in LED A-lamps cost about $1 each. At present the only Energy Star certified LED based A-lamp which provides a replacement for the 60 watt incandescent lamp uses no less than 18 power LEDs. It would be desirable to have a LED based A-lamp that can use fewer LEDs, while make the most of lumens available from the LEDs to provide the end user with superior task illuminance and use less electricity at the same time.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.